APPLICATION OF A MACROSCALE HYDROLOGIC MODEL TO ESTIMATE THE WATER-BALANCE OF THE ARKANSAS RED-RIVER BASIN

An approach for estimation of the parameters of a macroscale land surf ace hydrology model is illustrated for the Global and Water Cycle Expe riment (GEWEX) Continental Scale International Project (GCIP) large-sc ale area southwest (LSA-SW) which essentially comprises the Arkansas-R ed River basin. The macroscale land surface hydrology model parameters were estimated for 44 catchments within LSA-SW with areas ranging fro m 180 to 7100 km(2) using an automated search procedure. The catchment parameters were then linearly interpolated and overlaid on a one degr ee grid, which was used to represent the drainage network. The macrosc ale grid network model was run off-line at a daily time step, forced b y gridded station precipitation and potential evapotranspiration. The model-generated long-term mean streamflows were compared with observat ions (corrected for management effects such as reservoir storage and d iversions) and were found to agree to within one percent for the Arkan sas River and about two percent for the Red River. For both rivers, th e model underestimates the seasonal peak streamflow in late spring, an d overestimates the late summer and early fall minimum. Model-derived evapotranspiration, spatially averaged over the entire Arkansas-Red ba sin, was compared to evapotranspiration derived from an atmospheric mo isture budget of the Arkansas-Red River basin. On an average annual ba sis, for the period 1973-1986, the two agree to within one percent. Th e mean seasonal cycles for the two estimates agree quite closely from late winter to midsummer. However, the hydrologic model estimates less evapotranspiration in the fall, and more in midwinter, than the atmos pheric budget.